1. Field of the Invention
This application is generally directed towards pressure valves, and more particularly to a damage resistant valve assembly for inflatable tires.
2. Description of Related Art
Automotive rollover accidents due to tire blowouts are a major concern in the automotive, trucking, bussing and racing industries. Most recently the Firestone/Ford Explorer rollover problems have been of major concern to the public and industry, and have been at least partially attributed to tire blowouts. In addition to the bad publicity, the lost business, the loss in public good will and confidence, and the high costs of tire and automobile recalls may represent major financial costs to tire and automobile manufacturers. Thus any improvement in actual or publicly perceived tire quality would be a benefit.
The tire inflation valve, which is likely to be the least expensive part of any vehicle, is one potential cause of catastrophic tire failures. This is because the valve stem of the tire inflation valve necessarily protrudes from the metal (for example steel or aluminum) wheel to enable inflation and deflation of the tire by the operator or service person. The protruding valve stem contains the valve sealing surface near the tip of the valve stem. This is so that the control actuator of the valve sealing surface may be accessed by the inflation nozzle that is applied to the tip of the valve stem. As a result of the location of the sealing surface, any damage to the valve stem that occurs below the level of the valve sealing surface results in sudden and complete deflation of the tire. Any vehicle that loses pressure in any one of its tires results in an unbalanced condition that adversely affects the handling of the vehicle. Such loss of handling efficiency may result in a loss of control of the vehicle by the operator, with understandable bad consequences to the operator, passengers or bystanders. Such loss of control instances may also represent a large economic loss or injury to the vehicle operators and to anybody else who is involved in the incident, for example bystanders.
The commonly used valve stems in automotive wheels may be rubber molded tubes that surround threaded brass valve bodies into which valves are screwed. The valve stems are designed to be inserted through the metal wheel rim from what will be the inside of the tire. If the portion of the tire valve stem that protrudes from the metal wheel impacts an object such as a rock or a curb, the portion of the tire valve stem that is tom or ripped off may contain the valve body with the sealing surface, and thus result in sudden tire deflation. In addition, an impact may completely rip the entire valve stem out of the steel wheel rim, thus also resulting in sudden tire deflation, and thus provoking a potentially life-threatening incident. Such damage and impact may also be due to acts of vandalism such as striking the very exposed valve stem with a knife or hammer. The damage may result in immediate loss of tire pressure, which may be easily noticed, or it may result in a weakened valve stem, that is not easily noticed, which weakened valve stem may suddenly rupture during high speed driving, resulting in a loss of control incident.
The extent of this problem may be seen in the attempts made to prevent sudden loss of tire pressure in the NASCAR race circuit. It is known that at the high speeds the typical racecar tire filled with nitrogen may have steel valve stem ruptures or failures that may occur upon any substantial contact with another car, side barriers or curbs. As a result some racecars have tires that contain a separately inflated inner tire so that the loss of pressure in a valve stem rupture accident is not complete, and thus the driver may maintain control of the vehicle. However, the inner tire adds weight to the vehicle, and thus slows the car down and affects the ability to turn. In addition, the inner tire may only last a short time before it also deflates, is thus not a solution to the valve stem rupture sudden deflation problem.
The problem of sudden deflation is not simply a racecar or automobile collision problem, but may also occur during normal traffic instances, such as highway driving on hot road surfaces resulting in increased tire pressure and thus possible valve stem rupture at either a manufacturing flaw or the site of a prior cut or impact, such as by a rock. This is because, as noted above, that the valve stem may be made of rubber with a metal valve body near the external tip. Thus an increased gas pressure inside the tire may be transmitted to the hollow valve stem at the portion below the valve that is still outside the metal wheel, which due to previous damage or manufacturing defect may then rupture.
The valve stem may rupture even if it is not made of rubber. Brass or steel valve stems may be attached to the metal wheel rim using sealing rings and nuts on either or both of the outside and inside of the wheel. Such metallic valve stems are also subject to damage due to impacts, rocks and vandalism, and further may be susceptible to thermal expansion mismatch, corrosion, repetitive bending and vibrations which may cause stress cracking. These cracks and defects may be hidden from view on the inner surface of the valve stem, or at the juncture of the valve stem and metal wheel, until the valve stem suddenly breaks under the influence of some event and the tire pressure is abruptly lost.
The problem of accidental damage to inflation/deflation valves is not limited to automobile tires. Any inflated object may have a valve that when damaged may cause the object to suddenly lose pressure and deflate, often with serious repercussions. Pressurized vessels and tanks also may have external valves that allow for either pressurization or for venting. The possibility of damage to the external valve may result in loss of the contents of the vessel or tanks, with potential for substantial damage to the tank or the surrounding environment. Examples of such tanks or vessels include compressed natural gas tanks and tanker trucks, chemical tankers transporting or storing liquids such as acids, alkali materials, chlorine bleach, mercaptans, pesticides, herbicides, radioactive or industrial wastes, the accidental release of which would clearly be a major problem. Other gaseous materials include various petroleum gases, hydrogen sulfide, hydrogen cyanide, sulfur dioxide, and fluorocarbons, all of which may be regularly transported by truck or train tankers, or stored in tanks in the manufacturing plants, in the ordinary course of manufacturing business, but are also deadly to the environment if released. Thus the normal transportation and storage of liquids and gases may involve the use of valves of the type discussed herein for accessing and removing gases, and for pressurizing tanks with inert or ordinary gases for safe storage and transportation, and for improved speed of off loading of various liquid materials. Any of these valves may be damaged by collisions, corrosion, accidental impacts or other damage, and result in the inadvertent release of potentially hazardous materials.
Thus it would be a benefit to automobile tire users and users of pressurized vessels and tanks to provide a valve that does not open when damaged due to accidents, overpressure situations, manufacturing defects, or accidental impacts.